Glioblastoma, the most malignant form of glioma, results from a series of genetic lesions that include loss of heterozygosity for chromosome 17p, mutation of the p53 gone, overexpression of the platelet derived growth factor receptor, allelic losses of chromosome 22q, 13q (inclusive of the RB1 locus), and 19q and deletion of the interferon alpha and beta and CDKN2 loci on chromosome 9p. Two genetic lesions mark the transition from anaplastic astrocytoma (grade III) to glioblastoma: amplification and truncation of the epidermal growth factor receptor (EGFR) gene and losses of heterozygosity for chromosome 10, for which the phosphatase and tensin (PTEN) homology gene, located at 10q23.3 is one target. Deciphering the functional effects of mutations of these genes is an important step in understanding the transition from grade III glioma to glioblastoma. We will use human glioma cell lines expressing the tumor-specific truncated form of EGFR (EGFR*) and PTEN or mutant PTEN alleles to examine the mechanisms involved in this transition. Specifically we will: 1) dissect the role that tumor-associated alleles of PTEN and EGFR* play in the genesis and maintenance of the aggressive behavior of high-grade glioma. A combined biological and biochemical approach will be taken to construct mutant alleles of EGFR* and PTEN, genetically manipulate their expression and determine the effects of those manipulations on in vitro and in vivo tumorigenic behavior; 2) determine whether the effects of PTEN mutations are similar or different for earlier stages of tumor initiation and development. PTEN alleles expressed in a glial specific manner in transgenic mice will be assessed for tumor development singly or by crossing with mice carrying other mutations; 3) delineate pathway-specific molecules involved in EGFR* signaling. Genetic suppressor element, complementation technologies and protein-protein interactions will be employed to define elements of the EGFR* signaling cascade which enhance its proliferative or invasive effects in glioma cells; and, 4) compare transcriptomes between human glioma cells and mouse glioma models and glial lineages, cDNA array technology will be used to provide detailed transcriptomes for human cell lines expressing the mutant alleles, or mouse gliomas arising from their germline expression, to provide information bearing on the commonality or divergence of cellular gone expression responses to the presence of mutations, or combinations of mutations. These studies will provide significant information about the pathways by which glioblastomas emerge and targets for the design of rational therapies.